Processes and a device for determining the actual position of a structure of an object to be examined

ABSTRACT

A CT scanner is employed having a first coordinate system called the CT coordinate system related to the CT scanner for determining an actual position of a structure of an object to be examined. A coordinate measuring instrument (MI) is employed which is either a tactile or an optical or multisensor or an ultrasonic coordinate measuring instrument and which has a second coordinate system, the MI coordinate system, related to said coordinate measuring instrument. According to a variant, a) the coordinates of the object are determined in the MI coordinate system, b) the target position of the structure is predefined, c) after steps a) and b) the target position is determined in the MI coordinate system, d) and, the object is positioned in such a way that the target position of the structure comes to lie within a volume detected by the CT scanner using the result of step c).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of the patent applicationSer. No. 10/616,606, filed on Jul. 10, 2003 and issued as U.S. Pat. No.7,386,090 B2 on Jun. 10, 2008.

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BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to processes and to a device for determining theactual position of a structure of an object to be examined in acoordinate system.

(2) Description of Related Art including information disclosed under 37CFR 1.97 and 1.98

Computed tomography scanners serve to create three-dimensional images,namely, so-called CT scans, of objects such as, for example, workpiecesor human bodies or body parts, whereby these images also show internalstructures of the object.

In computed tomography technology, abbreviated as CT technology, X-raysare used to take images of an object or of a part thereof from manydifferent directions, that is to say, the object is X-rayed sequentiallyfrom many different directions. Thus, a computed tomography scanner,hereinafter referred to as a CT scanner, has an X-ray source and atwo-dimensional position-resolving detector, for example, a CCD matrix,that is sensitive to the radiation emitted by the X-ray source. TheX-ray source emits radiation, typically, for instance, of 450 keV. Theobject is positioned between the X-ray source and the detector and it isrotated incrementally with respect to the X-ray source or to the screen,or conversely, the CT scanner is rotated incrementally around theobject, which in this case remains stationary.

When it is not the CT scanner but rather the object that is rotated, theCT scanner generally has an object support stage on which the object isplaced. The object support stage can travel in such a way that theobject can be positioned in the beam path of the X-rays. Moreover, theobject support stage is rotatable so that the object can be rotated inorder to create the CT image. Typically, the object is rotated, forexample, in increments of 0.9° each, so that 400 rotation steps amountto a full revolution of the object. In this manner, the CT scanner candetect a certain volume that comprises either the entire object or apart thereof.

For each of the rotational positions that the object passes through, thedetector takes a two-dimensional transmission X-ray image of the object.On these two-dimensional images, the object appears larger than it is inreality since its size on the image corresponds to a centered projectionof the object on the detector surface, whereby the X-ray source is thecenter of projection.

Based on the array of two-dimensional individual images obtained in thismanner, a computer is used to calculate a three-dimensional digitalimage of the volume detected by the CT scanner, i.e. of the object or ofa part thereof, said image also showing internal structures that arecompletely enclosed in the object, insofar as these internal structureshave an absorption coefficient for the radiated X-rays that differs fromtheir surroundings, which is the case, for example, with cavities suchas drilled holes.

After each full revolution of the object, the object support with theobject can be shifted translatorily by a certain distance and theprocess explained above can be carried out again.

Such a commercially available CT scanner is described, for example, inthe brochure: “RayScan 3D-X-Ray Computed Tomography”, PRO-RS-A-E00011/01, made by Hans Walischmiller GmbH, D-88677 Markdorf, Germany.

Such CT scanners can be used to examine the internal structures ofobjects, for example, drilled holes in workpieces. In order to examine astructure of the object in this manner, first of all, a CT image of theentire object, including the structure of interest, can be created.

A drawback here is that, as a rule, the image of the structure onlyoccupies a small part of the image field of the CT scanner since the CTscanner can only achieve a limited relative spatial resolution. This isespecially due to the finite diameter of the exit pupil of the X-raysource and to the limited number of pixels of the CCD matrix; typically,a relative lateral resolution of, for example, 1:4000 can be achieved.

Therefore, in this case, a structure of the object whose extension is,for example, 1% of the object size, is only imaged at a relativeresolution of 1:40 which, in most cases, is insufficient for a detailedexamination of the structure.

Therefore, the CT image of the object can be used to determine thelocation of the structure within the object with respect to thecoordinate system of the CT scanner and to carry out a second CT scan ofthe object, while regulating the CT scanner in such a way that only theimmediate vicinity of the structure is detected by the CT scanner and asecond CT image of this vicinity is made with a greater magnificationfactor. In this manner, the relative resolution of the image of thestructure is enhanced, that is to say, more details of the structurebecome visible.

However, this also entails disadvantages. For example, it is a demandingprocedure to determine the location within the object on the basis ofthe first CT image. Moreover, such a localization of the structure isimprecise since not only the structure itself but also the surface ofthe object can only be detected with the limited resolution of the CTscanner, as a result of which the appertaining measuring uncertaintiesbecome greater.

Moreover, additional time is required to create the second CT image. Inview of the very high operating costs of a CT scanner, this need foradditional time is a substantial cost factor in examining the structure.

Furthermore, in order to create the second CT image, the object is onceagain exposed to a certain dose of ionizing radiation. This isespecially disadvantageous or problematic if the object consists ofliving biological matter. The repeated radiation exposure can also havea detrimental effect on non-living material. Ionizing radiation cantrigger, for example, ageing, transformation, discoloration ordegradation of plastics, it can have an altering effect on crystalstructures or it can destroy electronic modules.

BRIEF SUMMARY OF THE INVENTION

Therefore, the invention is based on the objective of creating a processand a device that allow a localization and examination of a structure ofan object so as to be less time-consuming and to allow greater precisionand reduced radiation exposure of the object.

This objective is achieved according to the invention by a process fordetermining the actual position of a structure of an object to beexamined in a coordinate system, whereby a CT scanner is employed whichuses CT technology, having a first coordinate system, the CT coordinatesystem, related to said CT scanner, and a coordinate measuringinstrument (MI) is employed which is either a tactile or an opticalcoordinate measuring instrument or a multisensor coordinate measuringinstrument or an ultrasonic coordinate measuring instrument, having asecond coordinate system, the MI coordinate system, related to saidcoordinate measuring instrument, whereby

-   a) the coordinates of the object to be examined are determined in    the MI coordinate system,-   b) a target position of the structure within the object to be    examined is predefined,-   c) after the execution of steps a) and b), the target position is    determined in the MI coordinate system,-   d) and, using the result of step c), the object to be examined is    positioned in such a way that the target position of the structure    comes to lie within the volume detected by the CT scanner.

Furthermore, this objective is achieved by a process for determining theactual position of a structure of an object to be examined in acoordinate system, whereby a CT scanner is employed which uses CTtechnology, having a first coordinate system, the CT coordinate system,related to said CT scanner, and a coordinate measuring instrument isemployed which is either a tactile or an optical coordinate measuringinstrument or a multisensor coordinate measuring instrument or anultrasonic coordinate measuring instrument, having a second coordinatesystem, the MI coordinate system, related to said coordinate measuringinstrument, whereby

-   a) the coordinates of the object to be examined are determined in    the CT coordinate system,-   b) a target position of the structure within the object to be    examined (1) is predefined,-   c) after the execution of steps a) and b), the target position is    determined in the CT coordinate system,-   d) and, using the result of step c), the object to be examined is    positioned in such a way that the target position of the structure    comes to lie within the area that can be detected by the coordinate    measuring instrument.

Moreover, the objective is achieved by a device for determining theactual position of a structure of an object to be examined in acoordinate system, with a CT scanner having a first coordinate system,the CT coordinate system, related to said CT scanner, and a coordinatemeasuring instrument is employed which is either a tactile or an opticalcoordinate measuring instrument or a multisensor coordinate measuringinstrument or an ultrasonic coordinate measuring instrument, having asecond coordinate system, the MI coordinate system, related to saidcoordinate measuring instrument, whereby the coordinates of the objectto be examined can be determined in the MI coordinate system, and atarget position of the structure within the object to be examined ispredefined, so that the target position can be determined in the MIcoordinate system, and the object to be examined can be positioned insuch a way that the target position of the structure comes to lie withinthe volume detected by the CT scanner, whereby the CT scanner and themultisensor coordinate measuring instrument are integrated into onesingle device.

Therefore, the first coordinate system is the CT coordinate system thatis related to the CT scanner. The second coordinate system is the MIcoordinate system; the latter is related to the coordinate measuringinstrument.

Therefore, in the process according to the invention for determining theactual position of a structure of an object to be examined in acoordinate system, a CT scanner is employed, having a first coordinatesystem, the CT coordinate system, related to said CT scanner, and acoordinate measuring instrument is employed which is either a tactile oran optical coordinate measuring instrument or a multisensor coordinatemeasuring instrument or an ultrasonic coordinate measuring instrument,having a second coordinate system, the MI coordinate system, related tosaid coordinate measuring instrument.

The device according to the invention for determining the actualposition and the shape of a structure of an object to be examined in acoordinate system comprises a CT scanner, having a first coordinatesystem, the CT coordinate system, related to said CT scanner, and acoordinate measuring instrument which is either a tactile or an opticalcoordinate measuring instrument or a multisensor coordinate measuringinstrument or an ultrasonic coordinate measuring instrument, having asecond coordinate system, the MI coordinate system, related to saidcoordinate measuring instrument.

According to a variant of the process, in the case of a predefinedtarget position of the structure, relative to at least three selected,non-co-linear points of the object to be examined, said object ispositioned using the coordinate measuring instrument in such a way thatat least a part of the object to be examined lies within the volumedetected by the CT scanner and this part of the object to be examinedcontains the target position of the structure.

Therefore, according to an embodiment of the device according to theinvention, in the case of a predefined target position of the structure,relative to at least three selected, non-co-linear points of the objectto be examined, said object can be positioned using the coordinatemeasuring instrument in such a way that at least a part of the object tobe examined lies within the volume detected by the CT scanner and thispart of the object to be examined contains the target position of thestructure.

The selected points can be located especially on the surface of theobject to be examined. The selected points can be marked, for example,by means of color, in order to facilitate their detection in the MIcoordinate system. Another possibility is to use, as the selectedpoints, those points that are designated on the basis of the geometry orshape of the object to be examined such as, for example, the cornerpoints.

In a variant of the process, at a predefined maximum deviation of thetarget position from the actual position of the structure of the objectto be examined, said object is positioned using the coordinate measuringinstrument in such a way that the target position as well as the actualposition of the structure lie within the volume detected by the CTscanner.

Therefore, according to an embodiment of the device according to theinvention, at a predefined maximum-deviation of the target position fromthe actual position of the structure of the object to be examined, saidobject can be positioned using the coordinate measuring instrument insuch a way that the target position as well as the actual position ofthe structure lie within the volume detected by the CT scanner.

The actual position of the structure can deviate from the targetposition, for example, as a result of manufacturing tolerances. Inactual practice, it is often possible to indicate the maximumanticipated or possible deviation of the actual position from the targetposition of the structure.

According to a variant of the process, the actual position differs fromthe target position by a predefined tolerance deviation at the most, sothat the actual position lies within a tolerance volume whose edge is ata distance from the target position by the tolerance deviation at themost, whereby the object to be examined is positioned using thecoordinate measuring instrument in such a way that the tolerance volumelies completely within the volume detected by the CT scanner.

In an embodiment of the device according to the invention, the actualposition differs from the target position by a predefined tolerancedeviation at the most, so that the actual position lies within atolerance volume whose edge is at a distance from the target position bythe tolerance deviation at the most, whereby the object to be examinedcan be positioned using the coordinate measuring instrument in such away that the tolerance volume lies completely within the volume detectedby the CT scanner.

In particular, the tolerance volume can be a sphere, a tolerance sphere,whose mid-point coincides with the target positions and whose radius ispredefined by the magnitude of the maximum deviation of the targetposition from the actual position of the structure.

According to a variant of the process, the object to be examined ispositioned using the coordinate measuring instrument in such a way thatthe volume detected by the CT scanner has, at the most, the x-foldvolume of the tolerance sphere or of the tolerance volume, whereby x isa predefinable number that is preferably greater than 1.

In a variant of the device according to the invention, the object to beexamined can be positioned using the coordinate measuring instrument insuch a way that the volume detected by the CT scanner has, at the most,the x-fold volume of the tolerance sphere or of the tolerance volume,whereby x is a predefinable number that is preferably greater than 1.

For example, the object to be examined can be positioned using thecoordinate measuring instrument in such a way that the volume detectedby the CT scanner is, at the most, two times the volume of the tolerancesphere or of the tolerance volume, which means that the number x in thisexample equals 2.

According to another example, the object to be examined is positionedusing the coordinate measuring instrument in such a way that the volumedetected by the CT scanner is, at the most, four times the volume of thetolerance sphere or of the tolerance volume, which means that the numberx in this example equals 4.

According to a variant,

-   -   in the case of a predefined target position of the structure,        relative to at least three selected, non-co-linear points of the        object to be examined (1), the object to be examined (1) is        positioned using the CT scanner in such a way that at least a        part of the object to be examined (1) lies within the area that        can be detected by the coordinate measuring instrument and this        part of the object to be examined (1) contains the target        position of the structure,    -   at a predefined maximum deviation of the target position from        the actual position of the structure of the object to be        examined (1), said object is positioned using the CT scanner in        such a way that the target position as well as the actual        position of the structure lie within the area that can be        detected by the coordinate measuring instrument, whereby the        actual position differs from the target position by a predefined        tolerance deviation at the most, so that the actual position        lies within a tolerance area whose edge is at a distance from        the target position by the tolerance deviation at the most,    -   the object to be examined (1) is positioned using the CT scanner        in such a way that the tolerance area lies completely within the        area that can be detected by the coordinate measuring        instrument.

The relative location and the relative orientation of the CT coordinatesystem relative to the MI coordinate system can be predefined or can bedetermined by means of calibration. Therefore, according to anembodiment, the relative location and the relative orientation of the CTcoordinate system relative to the MI coordinate system are predefined orcan be determined by means of calibration.

According to a variant, the following steps are carried out:

-   (i) by means of the coordinate measuring instrument, the location of    the at least three selected points of the object to be examined (1)    is determined relative to the MI coordinate system,-   (ii) the target position of the structure relative to the MI    coordinate system is calculated using the measured results obtained    in step (i), and-   (iii) the target position of the structure is converted from the MI    coordinate system to the CT coordinate system so that subsequently    the location of the target position in the CT coordinate system is    known.

According to an embodiment,

-   (i) by means of the coordinate measuring instrument, the location of    the at least three selected points of the object to be examined (1)    can be determined relative to the MI coordinate system,-   (ii) the target position of the structure relative to the MI    coordinate system can be calculated using the measured results    obtained in step (i), and-   (iii) the target position of the structure can be converted from the    MI coordinate system to the CT coordinate system so that the    location of the target position can be determined in the CT    coordinate system.

According to a variant, the object to be examined is positioned relativeto the CT scanner by means of a traveling mechanism, using the targetposition of the structure obtained by means of step (iii) with respectto the CT coordinate system, in such a way that the tolerance volume andthus also the structure lie within the volume detected by the CTscanner.

Therefore, according to an embodiment of the invention, the object to beexamined can be positioned relative to the CT scanner by means of atraveling mechanism, using the target position of the structure obtainedby means of step (iii) with respect to the CT coordinate system, in sucha way that the tolerance volume and thus also the structure lie withinthe volume detected by the CT scanner.

According to a variant, using the CT scanner, a three-dimensionaldigital CT image of the tolerance volume, including the structure, iscreated and stored as a CT data record, and the actual position of thestructure is determined in the CT coordinate system on the basis of theCT data record.

Therefore, according to an embodiment, using the CT scanner, athree-dimensional digital CT image of the tolerance volume, includingthe structure, can be created and stored as a CT data record, and theactual position of the structure can be determined in the CT coordinatesystem on the basis of the CT data record.

According to a variant,

-   (i) by means of the CT scanner, the location of the at least three    selected points of the object to be examined is determined relative    to the CT coordinate system,-   (ii) the target position of the structure relative to the CT    coordinate system is calculated using the measured results obtained    in step (i),-   (iii) the target position of the structure is converted from the CT    coordinate system to the MI coordinate system so that subsequently    the location of the target position in the CT coordinate system is    known,-   (iv) the object to be examined is positioned relative to the    coordinate measuring instrument by means of a traveling mechanism,    using the target position of the structure obtained by means of    step (iii) with respect to the MI coordinate system, in such a way    that the tolerance volume and thus also the structure lie within the    area that can be detected by the coordinate measuring instrument,-   (v) using the coordinate measuring instrument, a three-dimensional    digital image of the tolerance area, including the structure, is    created and stored as an MI data record, and the actual position of    the structure is determined in the MI coordinate system on the basis    of the MI data record.

According to a preferred variant of the process according to theinvention, the CT scanner used is one that has an X-ray source and atwo-dimensional, position-resolving detector having an active detectorsurface that is sensitive to the radiation emitted by the X-ray source,whereby the image field of the CT scanner is defined by the size of theactive sensor or detector surface, the target position of the structure,relative to at least three selected, non-co-linear points of the objectto be examined, is predefined and the actual position differs from thetarget position by a tolerance deviation at the most, so that the actualposition lies within a, for example, spherical tolerance volume whoseedge is at a distance from the target position by the tolerancedeviation at the most. The relative location and the relativeorientation of the CT coordinate system relative to the MI coordinatesystem here are either already known or else are determined by means ofcalibration.

The coordinate measuring instrument can be a tactile coordinatemeasuring instrument, that is to say, based on mechanical tracing, or anoptical coordinate measuring instrument or, for instance, a laser-aidedmultisensor coordinate measuring instrument or an ultrasonic coordinatemeasuring instrument. Thus, the coordinate measuring instrument canparticularly be one that is not capable of detecting internal structuresof the object to be examined.

According to this variant, the following steps are carried out:

-   a) by means of the coordinate measuring instrument, the location of    the at least three selected points of the object to be examined are    determined relative to the MI coordinate system,-   b) the target position of the structure relative to the MI    coordinate system is calculated using the measured results obtained    in step a),-   c) the target position of the structure is converted from the MI    coordinate system to the CT coordinate system, so that the location    thereof in the CT coordinate system is known,-   d) the relative position of the object to be examined is regulated    with respect to the CT scanner by means of a traveling mechanism,    using the target position of the structure obtained by means of    step c) relative to the CT coordinate system, in such a way that the    tolerance volume and thus also the structure lie within the volume    that can be detected by the CT scanner,-   e) by means of the CT scanner, a three-dimensional digital CT image    of the tolerance volume, including the structure, is created and    stored as a CT data record, and-   f) the actual position of the structure is determined in the CT    coordinate system on the basis of the CT data record.

This means that the CT scanner, using the measurements carried out bythe coordinate measuring instrument, the relative location and therelative orientation of the CT coordinate system and the MI coordinatesystem of the CT scanner can advantageously be regulated in such a waythat, right from the start, the structure is located in the area of theobject to be examined that is detected and imaged by the CT scanner.

According to a preferred embodiment of the device according to theinvention, the CT scanner has an X-ray source and a two-dimensionalposition-resolving detector having an active detector surface that issensitive to the radiation emitted by the X-ray source, whereby theimage field of the CT scanner is defined by the size of the activedetector surface, the target position of the structure, relative to atleast three selected, non-co-linear points of the object to be examined,is predefined, and the actual position differs from the target positionby a tolerance deviation at the most, so that the actual position lieswithin a, for example, spherical tolerance volume whose edge is at adistance from the target position by the tolerance deviation at themost, and the relative location and the relative orientation of the CTcoordinate system relative to the MI coordinate system are known or canbe determined by means of calibration, whereby

-   a) by means of the coordinate measuring instrument, the location of    the at least three selected points of the object to be examined can    be determined relative to the MI coordinate system,-   b) the target position of the structure relative to the MI    coordinate system can be calculated from this,-   c) the target position of the structure can be converted from the MI    coordinate system to the CT coordinate system, so that the location    thereof can be determined in the CT coordinate system,-   d) the relative position of the object to be examined relative to    the CT scanner can be regulated by means of a traveling mechanism,    using the target position of the structure relative to the CT    coordinate system, in such a way that the tolerance volume and thus    also the structure lie within the volume that can be detected by the    CT scanner, and-   e) the CT scanner can create a three-dimensional digital CT image of    the tolerance volume, including the structure, and can store it as a    CT data record,    so that the actual position as well as the shape of the structure    can be determined in the CT coordinate system on the basis of the CT    data record.

The term active detector surface refers to the surface of the detectorthat can be used to register the radiation from the X-ray source. Theterm image field of the CT scanner refers to the extension of theprojection of the volume detected by the CT scanner on the plane of thedetector surface.

Thus, according to the invention, the possibility is created to operatethe computed tomography scanner, CT scanner for short, at such a highmagnification that it can no longer synchronously image the entireobject to be examined, and in doing so, regulate the relative positionbetween the CT scanner and the object to be examined right from thestart in such a manner that advantageously the tolerance volume and thusalso the structure are always detected by the CT scanner.

In order to determine the target position of the structure relative tothe MI coordinate system, the measurement of at least three selectedpoints of the object to be examined relative to the MI coordinate systemis required; if more than three points are measured in theabove-mentioned manner, then the additional measured results canadvantageously be used to decrease the mean error and thus to increasethe achieved accuracy.

An advantage of the invention lies in the fact that the outer shape ofworkpieces or other objects, for example, in mass production, is alreadyoften routinely measured with a tactile or an optical coordinatemeasuring instrument or with a multisensor coordinate measuringinstrument, for example, for purposes of production monitoring. In thesecases, the results of step a) are available right from the start so thatstep a) does not involve any additional effort.

The tolerance volume can especially be rotation-symmetrical, i.e. atolerance sphere, so that its radius is defined by the tolerancedeviation and its mid-point is defined by the target position.

According to an advantageous variant of the invention, the CT scanner inprocess step d) is regulated in such a way that the center of thetolerance volume is essentially located in the center of the volume thatcan be detected by the CT scanner. Therefore, the CT scanner canpreferably be regulated in such a way that the center of the tolerancevolume is located essentially in the center of the volume that can bedetected by the CT scanner.

This means that the CT scanner is regulated according to the inventionin such a way that, right from the start, the target position of thestructure is advantageously in the center of the area of the object tobe examined that is detected and imaged by the CT scanner; the inventionmakes it possible to right away “center” the target position of thestructure in the area that can be detected by the CT scanner.

According to a variant, the CT scanner is regulated in such a way that,with the centered projection of the tolerance volume with the X-raysource as the center of projection, the image field is completely filledby the projection of the tolerance volume onto the detector, so that therelative lateral resolving power of the active detector surface is fullyutilized for detecting the tolerance volume. In this case, the CTscanner can be regulated in such a way that, with the centeredprojection of the tolerance volume with the X-ray source as the centerof projection, the image field is completely filled by the projection ofthe tolerance volume onto the detector.

According to another preferred variant, the CT scanner is regulated insuch a way that, with the centered projection of the tolerance volumewith the X-ray source as the center of projection, the smallest diameterof the projection of the tolerance volume onto the detector and thesmallest diameter of the image field of the CT scanner are essentiallyequal in size, or the largest diameter of the projection of thetolerance volume onto the detector and the largest diameter of the imagefield of the CT scanner are essentially equal in size.

According to another variant, the CT scanner is regulated in such a waythat, with the centered projection of the tolerance volume with theX-ray source as the center of projection, the largest diameter of theprojection of the tolerance volume onto the detector and the smallestdiameter of the image field of the CT scanner are essentially equal insize.

In a variant, the CT scanner can be regulated in such a way that, withthe centered projection of the tolerance volume with the X-ray source asthe center of projection, the smallest diameter of the projection of thetolerance volume onto the detector and the smallest diameter of theimage field of the CT scanner are essentially equal in size, or thelargest diameter of the projection of the tolerance volume onto thedetector and the largest diameter of the image field of the CT scannerare essentially equal in size.

According to another variant, the CT scanner can be regulated in such away that, with the centered projection of the tolerance volume with theX-ray source as the center of projection, the largest diameter of theprojection of the tolerance volume onto the detector and the smallestdiameter of the image field of the CT scanner are essentially equal insize.

In this manner, the magnification factor used to create the CT image canbe adapted to the dimensions of the image field and to the size of thetolerance volume in such a way that the projection of the tolerancevolume essentially corresponds to the size of the image field. In thismanner, the magnification factor can advantageously be selected in sucha way that it is the largest possible factor at which the tolerancevolume can still just barely be completely detected in its entirety bythe CT scanner so that, right from the start, the structure isadvantageously located in the area detected and imaged by the CTscanner. Therefore, even at a high magnification factor, there is norisk that the structure will lie outside of the area that can bedetected by the CT scanner. Here, the relative lateral resolving powerof the active detector surface is largely utilized for the detection ofthe tolerance volume.

The object to be examined can be, for example, a vehicle fuel-injectionnozzle with a typical length of 50 mm and a typical mean diameter of 25mm. The structure to be examined can be, for example, a hole that isdrilled in the fuel-injection nozzle and that is several millimeterslong.

In the case of such structures, which are systematically made in objectssuch as, for example, the drilled hole of a fuel-injection nozzle, thetarget position of the structure is likewise known right from the start.In many cases, the production of such objects is carried out with greatprecision, that is to say, with very small tolerances between the targetposition and the actual position, so that the tolerance volume is verysmall and the magnification factor can advantageously be selectedcorrespondingly high.

According to a variant,

-   A) the object to be examined is rotated incrementally around an axis    of rotation in order to create the CT image,-   B) for each of the rotational positions that the object to be    examined thus passes through, a two-dimensional transmission X-ray    image of the object to be examined is taken with the detector, and-   C) the three-dimensional CT image is created on the basis of the    two-dimensional transmission X-ray images thus obtained.

According to another variant,

-   D) after steps A) and B) have been carried out, the object to be    examined is shifted translatorily by a certain distance, preferably    in a direction parallel to the axis of rotation, and then once again    rotated incrementally around the axis of rotation;-   E) for each of the rotational positions that the object to be    examined passes through in step D), a two-dimensional transmission    X-ray image of the object to be examined is once again taken with    the detector, and-   F) another three-dimensional CT image is created on the basis of the    two-dimensional transmission X-ray image obtained in step E).

Steps D) to F) can be repeated several times.

According to another variant of the invention, in order to create athree-dimensional CT image, the object to be examined is not onlyrotated incrementally around a predefinable angle of rotation, butrather, after each of these rotation increments, it is shiftedtranslatorily by a certain distance so that the points of the object tobe examined that do not lie on the rotational axis describe anessentially spiral trajectory.

In addition to the location of the structure, the shape of the structurecan also be determined on the basis of the CT image or the CT datarecord. For example, the shape of the boundary surface of a smalldrilled hole in a fuel-injection nozzle can be measured very preciselyby means of the invention. Here, the target position of the structurecan be related to a selected point of the structure, whereby thecoordinates of additional points of the structure relative to this pointof the structure can be determined on the basis of the CT image. Thecoordinates of points of the structure determined in this way can beused, for instance, for the parameterization of the shape of thestructure.

According to another variant, the shape of the structure rather than thelocation of the structure is determined on the basis of the CT image orthe CT data record.

The relative location and the relative orientation between the MIcoordinate system and the CT coordinate system can be determined in thatthe position of at least three, preferably at least four, selected spacepoints of a calibration object is determined with the CT scanner in theCT coordinate system as well as with the coordinate measuring instrumentin the MI coordinate system. The comparison of the results thus obtainedmakes it possible to determine the relative location and the relativeorientation of the CT coordinate system relative to the MI coordinatesystem, for example, a transformation matrix for transforming these twocoordinate systems into each other. If more than three space points arethen calibrated in the manner described, the above-mentioned coordinatetransformation is mathematically overdetermined; the redundant results,however, can advantageously be combined in order to decrease the meanerror and thus to increase the precision achieved.

The object to be examined and the calibration object can, of course, beidentical. By the same token, the selected points of the object to beexamined can coincide with the space points used for the reciprocalcalibration of the two coordinate systems.

According to a preferred variant, the CT scanner and the multisensorcoordinate measuring instrument are integrated into one single device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 schematically shows an embodiment of a device according to theinvention for determining the actual position and the shape of astructure of an object to be examined 1 in a coordinate system.

DETAILED DESCRIPTION OF THE INVENTION

The device of FIG. 1 serves to determine the actual position and theshape of a structure of an object to be examined in a coordinate system.The device comprises a computed tomography scanner, hereinafter referredto as the CT scanner, with a coordinate system related thereto,hereinafter referred to as the CT coordinate system, and a multisensorcoordinate measuring instrument with a coordinate system relatedthereto, hereinafter referred to as the MI coordinate system.

The CT scanner comprises an X-ray source 5 and a two-dimensionalposition-resolving detector 6. The target position of the structure ispredefined relative to at least three selected, non-co-linear points ofthe object to be examined 1. The actual position of the structurediffers from the target position by a tolerance deviation at the most,so that the actual position lies within a, for example, spherical,tolerance volume whose edge is at a distance from the target position bythe tolerance deviation at the most. The relative location and therelative orientation of the CT coordinate system relative to the MIcoordinate system are known or can be determined by means ofcalibration.

By means of the coordinate measuring instrument, the location of the atleast three selected points of the object to be examined 1 can bedetermined relative to the MI coordinate system. The target position ofthe structure relative to the MI coordinate system can be calculatedfrom this. The target position of the structure can be converted fromthe MI coordinate system to the CT coordinate system, so that thelocation thereof can be determined in the CT coordinate system.

The relative position of the object to be examined 1 relative to the CTscanner can be regulated by means of a traveling mechanism 3, using thetarget position of the structure relative to the CT coordinate system,in such a way that the tolerance volume and thus also the structure liewithin the volume that can be detected by the CT scanner.

The CT scanner can create a three-dimensional digital CT image of thetolerance volume, including the structure, and can store it as a CT datarecord so that the actual position as well as the shape of the structurecan be determined in the CT coordinate system on the basis of the CTdata record.

The device of FIG. 1 comprises a computed tomography scanner,hereinafter referred to as a CT scanner, with an X-ray source 5 and atwo-dimensional position-resolving detector, namely, a CCD matrix 6,that is sensitive to the hard X-rays, typically, for example, of 450keV, emitted by the X-ray source 5. The device of FIG. 1 also comprisesa sensor-camera unit 4 that is arranged above the object to be examined1 and that comprises a mechanical tracer, a laser sensor as well as twocameras and that is part of a multisensor coordinate measuringinstrument.

The object to be examined 1 is located on a rotation table 2 that canrotate incrementally and that is, in turn, arranged on a traveling table3. Moreover, the rotation table 2 can be moved upwards and downwardstranslatorily, which is indicated by a vertical double arrow in FIG. 1.

The traveling table has a drive 9 and can be translatorily movedtwo-dimensionally, namely, in the plane perpendicular to the doublearrow of FIG. 1. The X-ray source 5, the CCD matrix 6, the sensor-cameraunit 4 as well as the traveling table 3 are arranged on a sharedassembly frame 7 that rests on a base 8 that can be leveled. By movingthe traveling table 3 in the direction of the X-ray source 5, themagnification factor is increased; by moving the traveling table 3 inthe opposite direction, the magnification factor is decreased.

The object to be examined 1 is arranged between the X-ray source 5 andthe CCD matrix 6 and, in order to create a CT image, is irradiated withthe radiation from the X-ray source 5, then rotated by turning therotation table 2, for example, by 0.9° and shifted translatorily by acertain distance by moving the traveling table 3, and then it isirradiated again, etc.

For each of the positions that the object to be examined 1 passesthrough, the CCD matrix 6 takes a two-dimensional transmission X-rayimage of the object to be examined 1 and, from the array oftwo-dimensional individual images thus obtained, a three-dimensionaldigital image of the area of the object to be examined 1 that wasdetected by the CT scanner is then calculated.

This calculation is performed by a calculation and control computer 10which, at the same time, serves to control the rotation table 2, thetraveling table 3, the sensor-camera unit 4 and the X-ray source 5 andwhich, for this purpose, is connected via lines 13, 14, 15, 16 to theabove-mentioned components. The X-ray source is supplied with electricpower via a connection cable 11 and can emit an X-ray beam cone 12 thatencompasses the object to be examined 1.

The CT scanner comprises the X-ray source 5, the CCD matrix 6, thecalculation and control computer 10, the rotation table 2, the travelingtable 3 with its drive 9, the assembly frame 7 and its base 8.

The multisensor coordinate measuring instrument comprises thesensor-camera unit 4, the calculation and control computer 10, therotation table 2, the traveling table 3 with its drive 9, the assemblyframe 7 and its base 8.

Accordingly, the calculation and control computer 10, the rotation table2, the traveling table 3 with its drive 9, the assembly frame 7 and itsbase 8 are associated with the CT scanner as well as with themultisensor coordinate measuring instrument. Thus, in the device of FIG.1, according to the invention, the CT scanner and the multisensorcoordinate measuring instrument are integrated into one single device.

The commercial applicability of the invention lies in the fact that itcan be used for nondestructive testing and monitoring of objects,especially mass-produced parts. The invention can likewise be used inmedical technology as well as in nondestructive material testing forlocating and measuring internal structures. The special usefulness ofthe invention is that enclosed structures in an object, for example,voids or cavities, can be located without destroying or opening theobject and can be measured right away with high precision as compared tothe prior art.

LIST OF THE REFERENCE NUMERALS

-   1 object to be examined-   2 rotating table-   3 traveling table-   4 sensor-camera unit-   5 X-ray source-   6 CCD matrix-   7 assembly frame-   8 base-   9 drive for the traveling table-   10 calculation and control computer-   11 connection cable of the X-ray source-   12 X-ray beam cone from the X-ray source-   13-16 lines

1. Method for determining the actual position of a structure of anobject (1) to be investigated in a coordinate system, wherein a computertomograph employing CT-technology with a first coordinate systemreferring to the computer tomograph, a CT-coordinate system, and acoordinate measurement instrument, which coordinate measurementinstrument is either a tactile or optical coordinate measurementapparatus, a multisensor coordinate measurement apparatus, or anultrasound coordinate measurement apparatus, with a second coordinatesystem referring to this coordinate measurement instrument, anMI-coordinate system, are employed wherein a) the coordinates of theobject (1) to be investigated are determined in the MI-coordinatesystem, b) a set point position of the structure within the object (1)to be investigated is pregiven, c) the set point position is determinedin the MI-coordinate system after performing the steps a) and b), d) andwherein the computer tomograph and the object (1) to be investigated arepositioned relative to each other under employing the determination ofstep c) that the set point position of the structure becomes to besituated within a volume captured by the computer tomograph, or aa) thecoordinates of the object (1) investigated are determined in theCT-coordinate system, bb) a set point position of the structure ispregiven within the object (1) to be investigated, cc) the set pointposition after performing the steps aa) and bb) is determined in theCT-coordinate system, dd) and the computer tomograph and the object (1)to be investigated are positioned relative to each other under theemployment of the determination of step cc) that the set point positionof the structure comes to be situated within the region capturable bythe coordinate measurement instrument.
 2. Method according to claim 1wherein the computer tomograph is positioned such under employing thedetermination of step c) that the set point position of the structurecomes to be situated within the volume captured by the computertomograph, or the computer tomograph such positioned according to stepdd) under employing the determination of step cc) that the set pointposition of the structure comes to be situated within the regioncapturable by the coordinate measurement instrument.
 3. Method accordingto claim 1, wherein, while referring to at least three selectednon-collinear points of the object (1) to be investigated of a pregivenset point position of the structure, the computer tomograph and theobject (1) to be investigated are positioned relative to each other withthe aid of the coordinate measurement instrument such that at least apart of the object (1) to be investigated is situated within the volumecaptured by the computer tomograph and this part of the object (1) to beinvestigated contains the set point position of the structure.
 4. Methodaccording to claim 1, wherein the computer tomograph and the object (1)to be investigated are positioned relative to each other with the aid ofthe coordinate measurement instrument with a pregiven maximum deviationof the set point position from the actual position of the structure ofthe object (1) to be investigated such that both the set point positionas well as also the actual position of the structure are situated in thevolume captured by the computer tomograph.
 5. Method according to claim4, wherein the actual position is different from the set point positionby at most a pregiven tolerance deviation such that the actual positionis situated within the tolerance volume, wherein an edge of thetolerance volume is removed from the set point position by at most thetolerance deviation, and the computer tomograph and the object (1) to beinvestigated with the aid of the coordinate measurement instrument arepositioned relative to each other such that the tolerance volume iscompletely disposed within the volume captured by the computertomograph.
 6. Method according to claim 5, wherein the tolerance volumeis a sphere, the tolerance sphere, wherein the center point of thetolerance sphere coincides with the set point position and wherein theradius of the tolerance sphere is pregiven by the amount of the maximumdeviation of the set point position from the actual position of thestructure.
 7. Method according to claim 5, wherein the computertomograph or the object (1) to be investigated are positioned relativeto each other with the aid of the coordinate measurement instrument suchthat the volume captured by the computer tomograph has at most an x-foldspacial contents of the tolerance sphere or, respectively, of thetolerance volume, wherein x is a pregivable number larger than
 1. 8.Method according to claim 1, wherein the computer tomograph and theobject (1) to be investigated are positioned relative to each other withthe aid of the computer tomograph in reference to at least threeselected non-collinear points of the object (1) to be investigated of apregiven set point position of the structure such that at least a partof the object (1) to be investigated is situated in the regioncapturable by the coordinate measurement instrument and this part of theobject (1) to be investigated contains the set point position of thestructure, the computer tomograph and the object (1) to be investigatedare positioned relative to each other with the aid of the computertomograph with a pregiven maximum deviation of the set point positionfrom the actual position of the structure of the object (1) to beinvestigated such that both the set point position as well as also theactual position of the structure are situated within the regioncapturable by the coordinate measurement instrument, the actual positionis different from the set point position by at most a pregiven tolerancedeviation such that the actual position is disposed within the toleranceregion, wherein the edge of the tolerance region is remote removed fromthe set point position by at most the tolerance deviation, and whereinthe computer tomograph and the object (1) to be investigated arepositioned relative to each other with the aid of the computer tomographsuch that the tolerance region is disposed completely within the regioncapturable by the coordinate measurement instrument.
 9. Method accordingto claim 3, wherein (i) the position of at least three selected pointsof the object (1) to be investigated relative to the MI-coordinatesystem is determined with the aid of the coordinate measurementinstrument, (ii) the set point position of the structure with referenceto the MI-coordinate system is calculated with the aid of themeasurement determinations obtained in step (i), and (iii) the set pointposition of the structure is re-calculated from the MI-coordinate systemto the CT-coordinate system, such that position of the set pointposition in the CT-coordinate system is known in the following. 10.Method according to claim 9, wherein the computer tomograph and theobject (1) to be investigated are controlled relative to each other byway of a traveling device (3) by using a set point position of thestructure with reference to the CT-coordinate system obtained accordingto step (iii) such that the tolerance volume and therefore also thestructure are disposed in the volume captured by the computer tomograph.11. Method according to claim 1, wherein a three-dimensional digitalCT-image of the tolerance volume inclusive the structure is generatedwith the aid of the computer tomograph and is stored as a CT-data setand wherein the actual position of the structure in the CT-coordinatesystem is determined from the CT-data set.
 12. Method according to claim8, wherein (i) the position of at least three selected points of theobject (1) to be investigated is determined relative to theCT-coordinate system with the computer tomograph, (ii) the set pointposition of the structure with reference to the CT-coordinate system iscalculated with the aid of the measurement determinations obtained instep (i), (iii) the set point position of structure is re-calculatedfrom the CT-coordinate system to the MI-coordinate system such that theposition of the set point position is known in the CT-coordinate systemin the following, (iv) the object (1) to be investigated and thecoordinate measurement instrument are controlled relative to each otherwith a traveling device (3) under employment of the set point positionof the structure with reference to the MI-coordinate system obtainedaccording to step (iii) such that the tolerance volume and thereforealso the structure is disposed in the region capturable by thecoordinate measurement instrument, and (v) a three-dimensional digitalimage of the tolerance region inclusive of the structure is generatedwith the aid of the coordinate measurement instrument and is stored as aMI-data set and the actual position of the structure in theMI-coordinate system is determined from the MI-data set.
 13. Methodaccording to claim 1, wherein such a computer tomograph is employedwhich has an x-ray source (5) and a two-dimensional spatially resolvingdetector (6), wherein the two-dimensional spatially resolving detector(6) has an active detector surface, wherein the active detector surfaceis sensitive to the x-ray radiation emitted by the x-ray source (5),wherein the image field of the computer tomograph is given by the sizeof the active detector surface, wherein the set point position of thestructure is pregiven with reference to at least three selectednon-collinear points of the object (1) investigated and wherein theactual position differs from the set point position by at most atolerance deviation, such that the actual position is disposed within asphere shaped tolerance volume, wherein the edge of the sphere shapedtolerance volume is removed from the set point position by at most thetolerance deviation, and the relative position and the relativeorientation of the CT-coordinate system relative to the MI-coordinatesystem is known or is determined by calibration, and wherein thefollowing steps are performed: a) the position of at least threeselected points of the object (1) to be investigated are determinedrelative to the MI-coordinate system with the coordinate measurementinstrument b) the set point position of the structure with reference tothe MI-coordinate system is calculated with the measurementdeterminations obtained in step a), c) the set point position of thestructure is re-calculated from the MI-coordinate system to theCT-coordinate system such a that the position of the set point positionis known in the CT-coordinate system, d) the relative position of theobject (1) to be investigated relative to the computer tomograph iscontrolled with a traveling device (3) by employing a set point positionof the structure with reference to the CT-coordinate system and obtainedaccording to step c) such that the tolerance volume and therefore alsothe structure are disposed in that volume, which volume the computertomograph is capable of capturing, e) a three-dimensional digitalCT-image of the tolerance volume inclusive the structure is generatedwith the aid of the computer tomograph and stored as a CT-data set, andf) the actual position of the structure in the CT-coordinate system isdetermined from the CT-data set.
 14. Method according to claim 13,wherein the tolerance volume is a tolerance sphere and such that theradius of the tolerance sphere is given by the tolerance deviation andthe center point of the tolerance sphere is given by the set pointposition.
 15. Method according to claim 13, wherein the computertomograph and the object (1) to be investigated are controlled relativeto each other according to method step d) such that the center of thetolerance volume is disposed essentially in the center of the volumecapturable by the computer tomograph.
 16. Method according to claim 13,wherein the computer tomograph and the object (1) to be investigated arecontrolled relative to each other such that the image field iscompletely filled by a projection of the tolerance volume onto thedetector in case of a centered projection of the tolerance volume withthe x-ray source (5) as a projection center.
 17. Method according toclaim 15, wherein the computer tomograph and the object (1) to beinvestigated are controlled relative to each other such that upon acentered projection of the tolerance volume with the x-ray source (5) asa projection center: the smallest diameter of the projection of thetolerance volume onto the detector and the smallest diameter of theimage field of the computer tomograph are essentially of the same size,the largest diameter of the projection of the tolerance volume onto thedetector and the largest diameter of the image field of the computertomograph are essentially of the same size, or the largest diameter ofthe projection of the tolerance volume onto the detector and thesmallest diameter of the image field of the computer tomograph are ofessentially the same size.
 18. Method according to claim 1, wherein inaddition to the position of the structure also the shape of thestructure is determined from the CT-image or the CT-data set.
 19. Methodaccording to claim 1, wherein the position of at least three selected onpoints of a calibration object are determined both with the computertomograph in the CT-coordinating system as well as also with thecoordinate measurement instrument in the MI-coordinate system andwherein the relative position and the relative orientation of theCT-coordinate system relative to the MI-coordinate system are determinedby comparison of the determinations obtained in this manner.
 20. Methodaccording to claim 19, wherein the object (1) to be investigated and thecalibration object are identical.
 21. Method according to claim 1,wherein A) the object (1) to be investigated is rotated stepwise arounda rotation axis for generating of the CT-image, B) a two-dimensionalthrough radiation x-ray image of the object (1) to be investigated istaken with the detector (6) for each of the rotation positions of theobject (1) to be investigated run through in this manner, and C) thethree-dimentional CT- image is generated of the two-dimensional throughradiation x-ray images obtained in this manner.
 22. Method according toclaim 21, wherein D) the object (1) to be investigated after performingthe steps A) and B) is shifted translationally by a certain distance inthe direction parallel to the rotation axis and thereupon the object (1)to be investigated is again rotated stepwise around the rotation axis;E) again a two-dimensional through radiation x-ray image of the object(1) to be investigated is taken with the detector (6) for each one ofthe rotation positions of the object (1) to be investigated run throughaccording to step D); and F) a further three-dimensional CT-image isgenerated from the two-dimensional through radiation x-ray imagesobtained according to step B).
 23. Device for determining the actualposition of a structure of an object (1) to be investigated in acoordinate system, with a computer tomograph with the first coordinatesystem referring to the computer tomograph, CT-coordinate system, and acoordinate measurement instrument, which either is a tactile or opticalcoordinate measurement apparatus, a multisensor coordinate measurementapparatus, or an ultrasound coordinate measurement apparatus, with asecond coordinate system referring to the coordinate measurementinstrument, MI-coordinate system, wherein the coordinates of the object(1) to be investigated are determinable in the MI-coordinate system andwherein a set point position of the structure within the object (1) tobe investigated is pregiven, such that the set point position isdeterminable in the MI-coordinate system, the computer tomograph and theobject (1) to be investigated are positionable relative to each otherwith the aid of the coordinate measurement instrument with reference toat least three selected noncollinear points of the object (1) to beinvestigated such that at least a part of the object (1) to beinvestigated is situated within the volume captured by the computertomograph and this part of the object (1) to be investigated containsthe set point position of the structure, wherein the set point positionof the structure comes to be situated within the volume captured by thecomputer tomograph, wherein the computer tomograph and the multisensorcoordinate measurement instrument are integrated to a single device. 24.Device according to claim 23, wherein the computer tomograph ispositionable with the aid of the coordinate measurement instrument withreference to at least three selected noncollinear points of the object(1) to be investigated of a pregiven set point position of the structuresuch that at least a part of the object (1) to be investigated issituated in the volume captured by the computer tomograph and this partof the object (1) to be investigated contains the structure, wherein theset point position of the structure comes to be located within thevolume captured by the computer tomograph.
 25. Device according to claim23, the computer tomograph and the object (1) to be investigated arepositionable relative to each other with the aid of the coordinatemeasurement instrument at a pregiven maximum deviation of the set pointposition from the actual position of the structure of the object (1) tobe investigated such that both the set point position as well as theactual position of the structure are situated in the volume captured bythe computer tomograph.
 26. Device according to claim 25, wherein theactual position differs from the set point position by at most apregiven tolerance deviation such that the actual position is disposedwithin the tolerance volume, wherein the edge of the tolerance volume isremoved from the set point position by at most the tolerance deviation,and the computer tomograph and the object (1) to be investigated arepositionable relative to each other with the aid of the coordinatemeasurement instrument such that the tolerance volume is containedcompletely in the volume captured by the computer tomograph.
 27. Deviceaccording to claim 26, wherein the tolerance volume is a sphere, thetolerance sphere, wherein the center point of the tolerance spherecoincides with the set point position and wherein the radius of thetolerance sphere is pregiven by the amount of the maximum deviation ofthe set point position from the actual position of the structure. 28.Device according to claim 26, wherein the computer tomograph and theobject (1) to be investigated are positionable relative to each otherwith the aid of the coordinate measurement instrument such that thevolume captured by the computer tomograph has at most the x-fold spacialcontents of the tolerance sphere or, respectively, of the tolerancevolume, wherein x is a pregiven number larger than
 1. 29. Deviceaccording to claim 23, wherein the relative position and relativeorientation of the CT-coordinate system relative to the MI-coordinatesystem are pregiven or are determinable by a measurement.
 30. Deviceaccording to claim 29, wherein (i) the position of the at least threeselected points of the object (1) to be investigated are determinablerelative to the MI-coordinate system with the coordinate measurementinstrument, (ii) the set point position of the structure with referenceto the MI-coordinate system is calculatable with the aid of themeasurement determinations obtained according to feature (i), and (iii)the set point position of the structure is re-calculatable from theMI-coordinate system to the CT-coordinate system such that the positionof the set point position is determinable in the CT-coordinate system.31. Device according to claim 30, wherein the object (1) to beinvestigated relative to the computer tomograph and the computertomograph are controllable relative to each other with the travelingdevice (3) under employment of the set point position of the structureobtained according to feature (iii) with respect to the CT-coordinatesystem such that the tolerance volume and therefore also the structureare disposed in the volume captured by the computer tomograph. 32.Device according to claim 23, wherein a three-dimensional digitalCT-image of the tolerance volume inclusive the structure is produceablewith the aid of the computer tomograph and is storable as a CT-data setand wherein the actual position of structure in the CT-coordinate systemis determinable from the CT-data set.
 33. Device according to claim 23,wherein the computer tomograph includes an x-ray source (5) and atwo-dimensional spatially resolving detector (6), wherein thetwo-dimensional spatially resolving detector (6) has an active detectorsurface, wherein the active detector surface is sensitive to the x-rayradiation emitted by the x-ray source (5), the image field of thecomputer tomograph is given by the size of the active detector surface,the set point position of the structure is pregiven relative to at leastthree selected noncollinear points of the object (1) to be investigatedand the actual position differs by at most the tolerance deviation fromthe set point position such that the actual position is disposed asphere shaped tolerance volume, wherein the edge of the tolerance volumeis removed by at most the tolerance deviation from the set pointposition, and the relative position and the relative orientation of theCT-coordinate system relative to the MI-coordinate system are known ordeterminable by measurement, wherein a) the position of the at leastthree selected points of the object (1) to be investigated relative tothe MI-coordinate system are determinable by way of the coordinatemeasurement instrument, b) the set point position of the structurerelative to the MI-coordinate system is calculatable from adetermination according to feature a), c) the set point position of thestructure is recalculatable from the MI-coordinate system to theCT-coordinate system such that the position of the set point position ofthe structure is determinable in the CT-coordinate system, d) therelative position of the object (1) to be investigated with respect tothe computer tomograph is controllable by way of a traveling device (3)under employment of the set point position of the structure with respectto the CT-coordinate system such that the tolerance volume and thereforealso the structure is disposed within that volume, which volume thecomputer tomograph is capable of capturing, and e) the computertomograph is capable to generate a three-dimensional digital CT-image ofthe tolerance volume inclusive the structure and to store the same as aCT-data set, such that the actual position as well as the shape of thestructure are determinable in the CT-coordinate system from the CT-dataset.
 34. Device according to claim 33, wherein the tolerance volume is atolerance sphere such that the radius of the tolerance sphere is givenby the tolerance deviation and the center point of the tolerance sphereis given by the set point position.
 35. Device according to claim 33,wherein the computer tomograph and the object (1) to be investigated arecontrollable relative to each other such that center of the tolerancevolume essentially is disposed in the center of the volume capturable bythe computer tomograph.
 36. Device according to claim 33, wherein thecomputer tomograph and the object (1) to be investigated arecontrollable relative to each other such that the image field is filledcompletely by the projection of the tolerance volume onto the detectorwith a centered projection of the tolerance volume with the x-ray source(5) as a projection center.
 37. Device according to claim 33, whereinthe computer tomograph and the object (1) to be investigated arecontrollable relative to each other such that upon a centered projectionof the tolerance volume with the x-ray source (5) as a projection centerthe smallest diameter of the projection of the tolerance volume onto thedetector and the smallest diameter of the image field of the computertomograph are essentially of the same size, the largest diameter of theprojection of the tolerance volume onto the detector and the largestdiameter of the image field of the computer tomograph are essentially ofthe same size, or the largest diameter of the projection of thetolerance volume onto the detector and the smallest diameter of theimage field of the computer tomograph are essentially of the same size.38. Method for determining the actual shape of a structure of an object(1) to be investigated in a coordinate system, wherein a computertomograph employing CT-technology with a first coordinate systemreferring to the computer tomograph, a CT-coordinate system, and acoordinate measurement instrument, which coordinate measurementinstrument is either a tactile or optical coordinate measurementapparatus, a multisensor coordinate measurement apparatus, or anultrasound coordinate measurement apparatus, with a second coordinatesystem referring to this coordinate measurement instrument, anMI-coordinate system, are employed wherein a) the coordinates of theobject (1) to be investigated are determined in the MI-coordinatesystem, b) a set point shape of the structure within the object (1) tobe investigated is pregiven, c) the set point shape is determined in theMI-coordinate system after performing the steps a) and b), d) andwherein the computer tomograph and the object (1) to be investigated arepositioned relative to each other under employing the determination ofstep c) that the set point shape of the structure becomes to be situatedwithin a volume captured by the computer tomograph, or aa) thecoordinates of the object (1) investigated are determined in theCT-coordinate system, bb) a set point shape of the structure is pregivenwithin the object (1) to be investigated, cc) the set point shape afterperforming the steps aa) and bb) is determined in the CT-coordinatesystem, dd) and the computer tomograph and the object (1) to beinvestigated are positioned relative to each other under the employmentof the determination of step cc) that the set point shape of thestructure comes to be situated within the region capturable by thecoordinate measurement instrument.